The Virgin Islands human population relies heavily on locally caught fish and, in fact, the demand for fish normally exceeds the local commercial harvest. The overharvest and subsequent decline in fish populations throughout the Virgin Islands is threatening to reduce this important source of protein to the island community especially to the lower income families, which rely heavily on locally caught fish. In an effort to ensure the sustainability of the fishery that supplies the bulk of affordable fish protein, we will focus our effort on groupers which are highly desirable in the market but also the most vulnerable to population collapse. One method of sustaining grouper populations is to establish marine fishery reserves to protect vulnerable grouper spawning aggregations. The overall goal of the proposed research is to evaluate the effect of variable levels of protection from fishing mortality on grouper breeding populations. The assessment will utilize a novel approach for measuring the condition of grouper breeding populations and will be used to develop a management model that will ensure the sustainabilityof grouper populations. Three red hind grouper (Epinephelus guttatus) spawning aggregation sites are known to occur in waters surrounding the USVI. One site is afforded year-round protection, one is protected seasonally and one has no protection from fishing mortality. The first objective of this study is to test the hypothesis that the density of spawning groupers at each aggregation site is directly related to level of protection from fishing mortality (i.e. high, medium or no protection). The second objective is to test the hypothesis that the size distribution, sex ratio and average size at sex change of spawning groupers depends upon the level of protection at each site. The third objective is to test the hypothesis that fecundity and reproductive output of each spawning population is directly related to level of protection. The final objective will be to validate the use of ultrasound imaging for determining the gender of other grouper species (e.g. Mycteroperca venenosa, E. striatus) and to establish a baselinefor evaluating the population response of these breeding aggregations to future management regulations. Documenting the effectiveness of marine fishery reserves and providing a framework for resource managers is critical for sustaining commercially important fish poplations and the continued health of the local VI community.